Field of the Invention
The present invention relates to a heat pump system for a vehicle, and more particularly, to a heat pump system for a vehicle which delays the change of the direction of a directional valve for a given period of time and then conducts the change of the direction of the directional valve, upon receiving the mode change signal between an air conditioner mode and a heat pump mode, thus preventing the generation of the noise and vibration caused by the differential pressure of a refrigerant.
Background of the Related Art
An air conditioner for a vehicle generally includes a cooling system for cooling the interior of the vehicle and a heating system for heating the interior of the vehicle. The cooling system is configured wherein air passing through the outside of an evaporator at the evaporator side of a refrigerant cycle is heat-exchanged with a refrigerant flowing to the interior of the evaporator and changed to cool air, thus making the interior of the vehicle cooled, and contrarily, the heating system is configured wherein air passing through the outside of a heater core at the heater core side of a cooling water cycle is heat-exchanged with cooling water flowing to the interior of the heater core and changed to hot air, thus making the interior of the vehicle heated.
Unlike the air conditioner for the vehicle, on the other hand, there is proposed a heat pump system which changes the direction of the flow of a refrigerant by using one refrigerant cycle to selectively conduct cooling and heating. For example, the heat pump system includes two heat exchangers (that is, an indoor heat exchanger disposed inside an air conditioner case to conduct heat exchanging between the refrigerant and the air blown to the interior of the vehicle and an outdoor heat exchanger disposed outside the air conditioner case to conduct heat exchanging) and a directional control valve adapted to change the direction of the flow of the refrigerant. If a cooling mode is activated through the change of the direction of the flow of the refrigerant made by the directional control valve, the indoor heat exchanger serves as a cooling heat exchanger, and if a heating mode is activated, the indoor heat exchanger serves as a heating heat exchanger.
Until now, various heat pump systems for a vehicle have been proposed, and one example of such conventional heat pump systems is shown in FIG. 1.
As shown in FIG. 1, the conventional heat pump system for a vehicle includes: a compressor 30 adapted to compress and discharge a refrigerant; an indoor heat exchanger 32 adapted to radiate the refrigerant discharged from the compressor 30; a first expansion valve 34 and a first directional valve 36 disposed in parallel with each other, the first expansion valve 34 being adapted to expand the refrigerant passing through the indoor heat exchanger 32 and the first directional valve 36 being adapted to allow the refrigerant passing through the indoor heat exchanger 32 to selectively flow to the first expansion valve 34; an outdoor heat exchanger 48 adapted to conduct heat exchanging between the refrigerant passing selectively through the first expansion valve 34 and outdoor air; an evaporator 60 adapted to evaporate the refrigerant passing through the outdoor heat exchanger 48; an accumulator 62 adapted to separate the refrigerant passing through the evaporator 60 into vapor refrigerant and liquid refrigerant; an internal heat exchanger 50 adapted to conduct heat exchanging between the refrigerant supplied to the evaporator 60 and the refrigerant returned to the compressor 30; a second expansion valve 56 adapted to selectively expand the refrigerant supplied to the evaporator 60; a bypass line 59 adapted to connect the outlet side of the outdoor heat exchanger 48 and the inlet side of the accumulator 62; and a second directional valve 58 disposed on the branch point of the bypass line 59.
In FIG. 1, a reference numeral 10 indicates an air conditioner case in which the indoor heat exchanger 32 and the evaporator 60 are disposed, 12 indicates a temperature adjusting door adapted to adjust the quantity of cool air and hot air mixed, indicates a blower disposed on the entrance of the air conditioner case, and 37 indicates a bypass line adapted to bypass the first expansion valve 34.
According to the conventional heat pump system for the vehicle under the above-mentioned configuration, if a heat pump mode (heating mode) is activated, the first directional valve 36 is changed in direction to allow the refrigerant to pass through the first expansion valve 34, and the second direction valve 58 is changed in direction to allow the refrigerant to pass through the second expansion valve 56. Further, the temperature adjusting door 12 operates as shown in FIG. 1. Accordingly, the refrigerant discharged from the compressor 30 passes through the indoor heat exchanger 32, the first directional valve 36, the first expansion valve 34, the outdoor heat exchanger 48, a high pressure part 52 of the internal heat exchanger 50, the second directional valve 58, the accumulator 62, and a low pressure part 54 of the internal heat exchanger 50, sequentially and returns to the compressor 30.
If an air conditioner mode (cooling mode) is activated, the first directional valve 36 is changed in direction to allow the refrigerant to bypass the first expansion valve 34, and the second direction valve 58 is changed in direction to allow the refrigerant to pass through the second expansion valve 56. Further, the temperature adjusting door 12 closes the passage of the indoor heat exchanger 32. Accordingly, the refrigerant discharged from the compressor 30 passes through the indoor heat exchanger 32, the first directional valve 36, the outdoor heat exchanger 48, the high pressure part 52 of the internal heat exchanger 50, the second expansion valve 56, the evaporator 60, the accumulator 62, and the low pressure part 54 of the internal heat exchanger 50, sequentially and returns to the compressor 30. That is, the evaporator 60 serves as an evaporator, and the indoor heat exchanger 32 closed by the temperature adjusting door 12 serves as a heater in the same manner as in the heat pump mode.
According to the conventional heat pump system, however, high pressure refrigerant is discharged to a low pressure by means of the differential pressure of the refrigerant upon the change between the heat pump mode and the air conditioner mode, which undesirably causes noise and vibration to be generated.
In the air conditioner mode, that is, the high temperature, high pressure refrigerant flows to the first directional valve 36, the bypass line 37 and the second directional valve 58, and the first expansion valve 34 and the bypass line 59 are in a low pressure. Upon the change from the air condition mode to the heat pump mode, at this time, the first directional valve 36 is changed in direction to allow the high temperature, high pressure refrigerant passing through the indoor heat exchanger 32 to flow to the first expansion valve 34 being in the low pressure, thus generating the noise and vibration due to the differential pressure of the refrigerant. The second directional valve 58 is changed in direction to allow the high temperature, high pressure refrigerant passing through the outdoor heat exchanger 48 to flow to the bypass line 59 being in the low pressure, thus undesirably generating the noise and vibration due to the differential pressure of the refrigerant.
In the heat pump mode, further, high temperature, high pressure refrigerant flows to the first directional valve 36, low temperature, low pressure refrigerant flows to the second directional valve 58, and the bypass line 37 and the second expansion valve 56 are in a low pressure. Upon the change from the air condition mode to the heat pump mode, at this time, the first directional valve 36 is changed in direction to allow the high temperature, high pressure refrigerant passing through the indoor heat exchanger 32 to bypass the first expansion valve 34 and to flow to the bypass line 37 being in the low pressure, thus undesirably generating the noise and vibration due to the differential pressure of the refrigerant.